Apparatus for treating a melt

ABSTRACT

An apparatus for treating a melt, especially a bath of molten steel or molten iron to be refined into steel in a ladle or the like, comprises a vessel containing the pulverulent material (e.g. a desulfurizing or nitrification substance) which is connected at its lower end with the upper end of a lance immersible in the melt. At the top of the lance there is provided a mixing chamber which is connected by a bypass duct to the top of the vessel while the bottom of the vessel is provided with a fluidizing or suspending compartment into which a carrier gas is admitted under pressure.

United States Patent 1191 Fiirster et al.

I APPARATUS FOR TREATING A MELT [75] Inventors: Eekehard Fiirster; Helmut Richter;

Edgar Spetzler; Jochen Wendorff, all of Oberhausen; Wilhelm Klapdar, Essen; Heinrich-Wilhelm Rommerswinkel, Mulheim-Ruhr, all of Germany [73] Assignee: Thyssen Niederrhein AG Huttenund Walzwerke, Qbcrhausen. Germany [22] Filed: Jan. 21,1974

[2 1] Appl. N0.: 435,096

[52] US. Cl. 266/34 :1; 302/53 [51] Int. Cl C2lc 7/00 [58] Field of Search 1. 75/51. 52; 266/34 T, 34 A; 302/53, 54, 55

[56] References Cited UNITED STATES PATENTS 2 734,782 2/l956 Gallc 302/53 2.858.125 l(l/l958 Clcnny ct all... 266/34 T 3.001.864 9/l96l Mullcr ct al 11 266/34 T 0 95 L I T 6 10 1111 3,891,196 June 24, 1975 3.194539 7/l965 Hannc-Wiamc 75/51 x 3.4321011 3/1969 Hill ct 111. 302/53 3.459.536 8/1969 Ttlulilllll ct 111 266/34 A FOREIGN PATENTS OR APPLICATIONS 1.035907 8/1958 Germany .1 2661/34 T l,8l7 5(17 12/1967 Germany 302/53 Primary Examiner-Gerald A. Dost Attorney Agent, or Firm-Karl F. Ross; Herbert Dubno [57] ABSTRACT An apparatus for treating a melt, especially a bath of molten steel or molten iron to be refined into steel in a ladle or the like, comprises a vessel containing the pulverulent material (e.g. a desulfurizing or nitrifica tion substance) which is connected at its lower end with the upper end of a lance immersible in the melt. At the top of the lance there is provided a mixing chamber which is connected by a bypass duct to the top of the vessel while the bottom of the vessel is provided with a fluidizing or suspending compartment into which a carrier gas is admitted under pressure.

6 Claims, 5 Drawing Figures PATENTEDJHN 24 I975 SHEET 1 APPARATUS FOR TREATING A MELT FIELD OF THE INVENTION The present invention relates to apparatus for treating a metallurgical bath and, more particularly, to a system for injecting comminuted or pulverulent finely divided solids into a steel bath or melt for desulfurizing, nitrification and like alloying or refining purposes.

BACKGROUND OF THE INVENTION Numerous techniques have been provided heretofore for the introduction of solids into a metallurgical melt and especially a bath of molten steel or molten iron to be refined into steel and contained in a crucible or ladle.

The problems involved in integrating a solid into the melt are numerous and are well-known in the art. For example. when the solid has a density less than that of the melt, it cannot be cast upon the melt surface and be expected to be integrated into the molten metal since it will invariably float upon the surface. Complex means must be used to stir the melt or otherwise bring the solids into contact with the inner portions of the bath Even solids which have a density greater than that of the molten metal cannot be effectively incorporated into the bath by casting them in granular form upon the melt surface if the melt is covered by a slag since adhesion of the slag to the solids also causes the additive to float. Where entrainment of the slag into the body of the melt is undesirable. moreover. the agitation techniques mentioned above cannot be used.

It has been proposed to blow the additive onto the surface of the molten-metal bath from lances or nozzles trained upon the surface of the melt. In this case, the

particulate matter is entrained in a carrier gas and is transported thereby onto and below the surface of the melt. In this system as well a complete integration of the solids is not possible or may only be local in nature, ie, confined to surface zones.

It is known to introduce finely divided treating agents such as desulfurizing substances and nitrification agents into the body of a steel melt in a carrier gas by so-called immersion lances" which are plunged through the surface of the melt and have a mouth open ing into the interior of the melt close to the bottom thereof. The particulate matter is entrained in a carrier gas, preferably an inert gas such as argon. although nitrogen may be used when nitrification is desired.

In the usual apparatus of this type, the outlet ofa vessel containing the particulate matter is connected directly to the lance and a carrier gas is supplied to the latter to entrain the particulate material through the lance and into the melt at the mouth of the latter.

When the mouth of the lance is located at a depth of 2000 mm or greater below the surface of the melt, variations in the pressure of the carrier gas at the mouth may arise, these pressure variations resulting in increased feed rates from time to time and/or passage of the molten metal into the bore of the lance.

It will be apparent that the immersion lance, which is provided with a shell or sheath of refractory material. which may be water-cooled, is relatively expensive so that penetration of molten metal into the bore and solidification therein to plug the lance may require replacement of an expensive element of the system. Furthermore. the mechanical action on the lance resulting from pressure fluctuations itself may cause deterioration of the latter.

In practice, it is desirable to use immersion lances which introduce the particulate material to a depth of 2000 mm or more and with a length of 4000 to 5000 mm and. with such lances, the conventional systems for supplying the particulate material have proved to be unsatisfactory OBJECTS OF THE INVENTION It is the principal object of the present invention to provide an improved apparatus for the introduction into a melt of finely divided solid treating and alloying agents using an immersion lance at whose mouth or end a substantially constant pressure can be maintained without difficulty and which is of particular utility for immersion lances of great length and large immersion depths.

Another object of the invention is to provide a system for injecting finely divided desulfurizing and nitrifying substances into a molten steel bath using immersion lances adapted to remain in the melt for periods of 5 to l0 minutes at temperatures of at least [530C Still another object of the invention is to provide an improved system for feeding particulate solids to an immersion lance whereby the aforementioned disadvantages can be obviated.

SUMMARY OF THE INVENTION The invention, which attains the aforedescribed objects. comprises an apparatus for the introduction of finely divided solid treating agents (especially pulverulent desulfurizing substances and nitrification agents) into steel melts using a carrier gas, the apparatus comprising a source of the carrier gas (e.g. a battery of carrier-gas cylinders or flasks), a supply vessel or receptacle for the finely divided or pulverulant solid treating agent, means forming a Suspender or suspension chamber at the lowest part of this vessel and provided with a carrier-gas inlet and a solid/gas suspension outlet, and an immersion lance connected by a conduit, duct or pipe to the latter.

The invention comprises providing this conduit with a mixing chamber which permits injection of a pressurizing gas into the suspension stream, the mixing chamber being provided with a bypass duct having a control valve and connected with the head of the supply vessel.

In the system, according to the present invention, the pressure at the end or at the mouth of the immersion lance is established by the adjustment of the control valve in the bypass duct. This control valve may thus serve for regulating the pressure at any desired level and, once set. permits automatic regulation of the pressure so that it is maintained constant.

When the supply pressure of the carrier-gas battery is constant, the valve acts simply as a regulating valve which is adjustable to set the pressure. In general, a certain minimum quantity of the treating agent must be provided in the vessel and the latter is simple to establish The pressure at the mouth of the end of the lance can be held constant with great precision so that fluctuations in pressure and the mechanical disadvantages thereof are avoided.

It is especially important that the system completely exclude sudden pressure drops which can cause molten metal to flow into the bore or passage of the lance.

According to another feature of the invention. a direct connection is provided between the mixing chamber and the carrier-gas battery or another source of carrier gas by a duct formed with a control valve. The latter arrangement has been found to be especially desirable when the apparatus is to provide a pressure at the outlet of the lance which is only slightly above the hydrostatic pressure of the melt at this outlet.

It has been found to be desirable to minimize the pressure loss in the mixing chamber by providing the latter as a cylindrical housing into which the suspension-feed duct passes axially while the bypass duct opens tangentially. The feed line or duct in the region of the mixing chamber is provided with one or more carrier-gas inlet openings which may be disposed in an annulus. i.e. circumferentially and can be circumferentially elongated. The inlet openings thus may be one or more circumferential slits or a plurality of slits spaced circumferentially around the feed line or duct.

It has been found to be advantageous, moreover. to prevent variation of the geometric locations of the lance. vessel and feed line and especially variations in the relative positions of these elements and the mixing chamber. Accordingly, it is preferred to provide the mixing chamber directly upon the immersion lance and to connect the immersion lance rigidly to the vessel for joint vertical movement relative to the bath.

The system has the advantage that the pressure at the end or the mouth of the immersion lance can be maintained constant without complicated control devices at any desired level. The carrier gas stream which flows through the bypass duct and the treatment agent in the supply vessel is substantially uniformly throttled and is easily regulated by the control valve to establish any desired pressure at the mouth of the immersion lance with precision. During the operation of the suspending means. this relationship is not affected and uniformity throughout the injection process is ensured.

Simultaneously. a highly uniform feed rate of the treating agent is ensured, i.e. the rate at which material is fed to the bath can be maintained with great precision. It is not necessary. therefore, to provide complex solid-feed devices as have been required heretofore.

Another advantage of the present system is that the quantity of carrier gas which is necessary to entrain a given quantity of particulate matter into the melt is lower than has been necessary heretofore. The feed is completely automatic since the gas returned by the bypass duct is directly related to the pressure of the gas in the feed line.

Still a further advantage of the system of the present invention is to be found in the fact that the suspension is fed to the upper portion of the lance which is not under thermal stress. Moreover. the particle feed takes place substantially without a lag in spite of the fact that a cushion of the treating agent is maintained in the supply vessel. The system also can be operated so as to substantially free from the injector or venturi effect.

It is self-understood that the applied pressure must be a function ofthe total length of the lance and its immersion depth and that the system can operate with opentop or closed top (covered) vessels. the latter being em ployed for the vacuum treatment of steel.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects. features and advantages of the present invention will become more readily apparent from the following description. reference being made to the accompanying drawing in which:

FIG. I is a vertical elevational view. partly in diagrammatic form. of an apparatus illustrating the principles of the present invention;

FIG. 2 is a section taken along the line llll of FIG. and drawn to a larger scale;

FIG. 3 is a section taken along the line IlIllI of FIG. 2 and drawn to the same scale as the latter;

FIG. 4 is an enlarged detail view of the suspending portion of the apparatus of FIG. 1'. and

FIG. 5 is a view similar to FIG. 3 but illustrating another embodiment of the invention.

SPECIFIC DESCRIPTION In FIG. I there is illustrated an apparatus for the injection of finely divided particulate matter. especially desulfurizing and nitrification agents. into a steel melt using a carrier gas. The apparatus essentially comprises a carrier-gas battery I. a supply vessel 2 for the finely divided treating agent. a suspending chamber 5 provided at the lowest portion of the vessel 2, a carrier-gas inlet 3 opening into the suspending chamber and an outlet 4 for leading the solid/gas suspension out of the suspending chamber and via a supply line or duct 7 into the mixing chamber 9 formed at the top of an immersion lance 6. The latter is adapted to be immersed into a bath I6 of molten steel contained in a ladle 30.

The suspending chamber 5 is. as shown in FIG. 4. provided with a perforated wall 8 overlying an annular opening 3] in the downwardly converging funnel shaped bottom 32 of the vessel 1. An annular housing 33 communicates with the opening 3] and is fed with the carrier gas via the inlet 3. The housing 33 thus distributes the carrier gas all around the wall 32. The suspending means 5 operates in accordance with fluidized bed principles. In other words. the carrier gas introduced through the perforated wall 8 entrains the fine particles in a turbulent or vortex movement which is maintained continuously and produces the solid/air suspension which is drawn off through the outlet 4.

The mixing chamber 9 permits the introduction of a pressure gas into the suspension stream. either from the supply battery 1 via a pipe 34 and a control valve 35 leading to a flexible hose 36 communicating with the chamber 9 or from another supply source 37 via its valve 38 which likewise communicates with the flexible hose 36.

The mixing chamber 9 is connected by a bypass duct II) with a control valve 11 to the head of the supply vessc] 2.

FIGS. 2 and 3 illustrate the configuration of the mixing chamber 9. The mixing chamber 9 comprises a cylindrical housing 12 through which the suspension-fed pipe 7 extends axially. The bypass duct II) opens tangentially into the mixing chamber 9.

The suspension-feed pipe 7 is provided within the housing 12 with a plurality of carrier-gas inlet openings 13 arranged with circumferential spacing around the pipe 7. An injector of the venturi type can. of course. also be provided within this mixing chamber. The mixing chamber 9 is provided directly upon the upper end of the immersion lance 6 which is connected by auxiliary means. e.g. a beam I4, rigidly with the supply vessel 2 for joint vertical movement of the supply vessel and the lance.

To this end. a post is provided to form rails upon which a carriage 39 is vertically displaceable. the carriage carrying a plate 40 upon which the beam 14 and the vessel 2 are rigidly secured. A winch engine 41 has its drum 42 adapted to reel out or in a cable 43 passing over a direction-changing pulley 44 at the top of the upright 15, the cable being anchored at 45 to the car riage.

A reducing valve 17 at the carrier-gas battery 1 delivers a constant supply pressure to the system and, by ad justmcnt of the valve 11, the discharge pressure at the mouth of the lance 6 is maintained constant. The lance may be lowered to a depth of 2000 mm or more into the ladle as represented by dot-dash lines in FIG. 1. Valve ll may be a simple throttle valve. a pressurerelief valve or a control valve having an appropriate control circuit connected thereto.

A valve 18 below the suspending device 5 serves only to cut off the flow of the suspension or to commence such flow since it need not provide any control functiotr Of course, control circuits may be provided to 0p erate the valves in response to flow rate sensors in the feed pipe 9 and the bypass duct 10 if greater precision is required.

In FIG. 5, there is shown a system in which the carrier gas inlets 13 are replaced by an annular opening 46 or by circumferential rows of cireumferentially elongated slits 47. i

We claim:

1. An apparatus for introducing particulate solids into a molten-metal melt. comprising:

a supply vessel receiving solid particles and formed at its bottom with a suspending device for forming a solid/gas suspension, means for admitting a car rier gas into said suspending device. and an outlet at said suspending device for discharging said suspension from said vessel;

a lance immersibly in said bath;

a suspensionfeed line connecting said outlet with said lance;

a mixing chamber along said feed line for admitting a pressure gas to the suspension stream traversing said feed line; and

a bypass duct provided with a control valve connecting the top of said vessel with said mixing cham her, said mixing chamber comprising a cylindrical hous ing spacedly surrounding said feed line. said bypass duct opening tangentially into said housing and said feed line being provided within said housing with at least one carrier gas opening.

2. The apparatus defined in claim 1. further comprising means including another control valve directly connecting a source of carrier gas to said mixing chamber.

3. The apparatus defined in claim 1 wherein said housing is mounted directly on the upper end of said immersion lance.

4. The apparatus defined in claim 3, further comprise ing means rigidly connecting said immersion lance and said vessel for joint vertical movement.

5. The apparatus defined in claim 4. further comprising an upright, a carriage vertically displaceable on said upright and means for mounting both said vessel and said lance upon said carriage. and source being an inert carrier-gas battery connected solely to said suspending device.

6. The apparatus defined in claim 5 wherein said suspending device comprises a downwardly tapering conical wall formed on said vessel and provided with an annular opening. means defining an annular chamber communicating with said opening and connected to said battery. and a perforated wall spanning said open- 

1. An apparatus for introducing particulate solids into a molten-metal melt, comprising: a supply vessel receiving solid particles and formed at its bottom with a suspending device for forming a solid/gas suspension, means for admitting a carrier gas into said suspending device, and an outlet at said suspending device for discharging said suspension from said vessel; a lance immersibly in said bath; a suspension-feed line connecting said outlet with said lance; a mixing chamber along said feed line for admitting a pressure gas to the suspension stream traversing said feed line; and a bypass duct provided with a control valve connecting the top of said vessel with said mixing chamber, said mixing chamber comprising a cylindrical housing spacedly surrounding said feed line, said bypass duct opening tangentially into said housing and said feed line being provided within said housing with at least one carrier gas opening.
 2. The apparatus defined in claim 1, further comprising means including another control valve directly connecting a source of carrier gas to said mixing chamber.
 3. The apparatus defined in claim 1 wherein said housing is mounted directly on the upper end of said immersion lance.
 4. The apparatus defined in claim 3, further comprising means rigidly connecting said immersion lance and said vessel for joint vertical movement.
 5. The apparatus defined in claim 4, further comprising an upright, a carriage vertically displaceable on said upright and means for mounting both said vessel and said lance upon said carriage, and source being an inert carrier-gas battery connected solely to said suspending device.
 6. The apparatus defined in claim 5 wherein said suspending device comprises a downwardly tapering conical wall formed on said vessel and provided with an annular opening, means defining an annular chamber communicating with said opening and connected to said battery, and a perforated wall spanning said opening. 